Anaemia is common and is usually the normocytic, normochromic anaemia of chronic disease. Deficiency of iron and/or folate also occurs. Despite terminal ileal involvement in Crohn’s disease, megaloblastic anaemia due to vitamin B\2 deficiency is unusual, although the vitamin B’2 level can be low. There is often a raised erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) and a raised white cell count. Hypoalbuminaemia is present in severe disease. Liver biochemistry may be abnormal. Blood cultures are required if septicaemia is suspected.
These should always be performed on presentation if diarrhoea is present.
CROHN’S DISEASE. A small bowel follow-through is usually performed first unless the disease is predominantly Crohn’s colitis.
A small bowel follow-through shows an asymmetrical alteration in the mucosal pattern with deep ulceration and areas of narrowing (string sign) largely confined to the ileum. Skip lesions with normal bowel between are also seen.
Barium enema has been superseded by colonoscopy, if this is available, for colonic disease. Early changes on barium enema consist of aphthous ulceration; this involvement is again usually patchy with deep ulceration developing later.
Ultrasound and CT scanning are helpful in delineating abscesses, masses, thickened bowel wall and mesentery, or other extraluminal problems in Crohn’s disease.
ULCERATIVE COLITIS. A plain X-ray of the abdomen is performed in severe colitis cases to look for colonic dilatation. The extent of the disease can be judged by the air distribution in the colon.
In an instant, unprepared barium enema, barium is run into the rectum without pressure and a single film taken. This is a good investigation to show the extent of the disease. Barium enema is again being superseded by colonoscopy. If performed, there may be ulceration and in longstanding disease the colon is shortened and narrowed . The disease is usually continuous.
In Crohn’s disease, this is performed if colonic involvement is suspected when biopsies of the whole colon can be taken. In ulcerative colitis, colonoscopy shows the exactextent of the disease and, again, biopsies from the whole colon and ileum can be taken to differentiate between Crohn’s disease and ulcerative colitis.
Small bowel function tests
When Crohn’s disease involves the small bowel, other tests may be necessary, e.g. a breath test for bacterial overgrowth or a test for vitamin Bl2 absorption.
ACTIVITY OF DISEASE
A rough estimate of the activity can be made on the clinical picture and laboratory tests of ESR, serum albumin and acute-phase protein (e.g. CRP or orosomucoids). In some centres scans to localize areas of inflammation are performed using radiolabelled leucocytes injected intravenously; these may help in localizing abscesses.